Both situations are "emergencies" - to a greater or lesser degree. And yet there are some very significant differences between the two and how this will affect the way in which businesses should approach online Pay Per Click (PPC) advertising.

Here's the thing.... if you don't have toothache and you haven't lost your keys you are unlikely to be searching for either of these two services. I've never met anyone who saw an ad for a dentist and thought - "Cool - I think I'll go get a filling".

You need them when you need them. But - and here's the significant point in all of this - most people have a dentist. Very few people have a locksmith.

Here's what I'm betting... when you needed the dentist you rang your dentist. When you needed a locksmith you Googled one.

Let's consider that for a moment. Search advertising relies upon a person using Google to search on keywords - so if I'm a locksmith - then I need to be bidding on keywords such as, well, "locksmith" and look to have my ad appear (and appeal) to people when the search results come up.

But in the case of the dentist people are unlikely to search. As we've established, most people already have a dentist and if they do resort to search then they will probably be searching fairly specifically to find their dentist's contact numbers.

So what does this mean for advertisers?

Let's consider the locksmith first of all - since they are at one end of a continuum with all search at one end and all, display at the other. Display ads, by the way are the text and image ads which appear on websites as you surf the net. They are not triggered by searches but rather by the kind of content found on the pages (ads for pet supplies on a blog page about pet care) or for demographic reasons (ads for high heeled sneakers on women's interest pages). The locksmith knows that most people will search for a locksmith. After all, you just need to get into your house - there's probably little to chose between locksmiths, so you look for the one that is nearest, or is a name you recognize from seeing their van, etc. Thus for the locksmith, search is going to be very important.

The dentist on the other hand, is not going to see the bulk of his online traffic coming from search. Sure - there will be some. People who are new to the area, for example, but beyond these people, few are going to be running a search.... unless, and here is the key, they are not completely happy with their current dentist. Maybe their last experience was below par, maybe she just moved, maybe she raised her prices - could be a number of reasons. So an element of search could well be a good thing.

But there is going to be another group of people who are not happy with their current dentist but who are not actively searching for an alternative. And it is this group which offers the most potential. They are not searching, so the only way to reach them is through display advertising.

Having established the profile of these people, i.e. they are not happy with their current dentist, we can immediately see an initial approach - an ad with a headline along the lines of "Not Happy with Your Current Dentist?" - if nothing else that kind of headline will - excuse the pun - strike a nerve!

So consider search and display as complimentary. Many businesses dismiss one or the other as not working for their business. But in most cases both can be made to work with a little thought as to the client profile - Why are they in the market? When are they in the market? And, how can we reach them?